A comprehensive study of short bursts from SGR 1806-20 and SGR1900+14 detected by HETE-2

Yujin E. Nakagawa*, Atsumasa Yoshida, Kevin Hurley, Jean Luc Atteia, Miki Maetou, Toru Tamagawa, Motoko Suzuki, Tohru Yamazaki, Kaoru Tanaka, Nobuyuki Kawai, Yuji Shirasaki, Alexandre Pelangeon, Masaru Matsuoka, Roland Vanderspek, Geoff B. Crew, Joel S. Villasenor, Rie Sato, Satoshi Sugita, Ju N Ichi Kotoku, Makoto ArimotoGraziella Pizzichini, John P. Doty, George R. Ricker

*この研究の対応する著者

研究成果: Article査読

40 被引用数 (Scopus)

抄録

Temporal and spectral studies of short bursts (≲ a few hundred milliseconds) are presented for the soft gamma repeaters (SGRs) 1806-20 and 1900+14 using the HETE-2 samples. In five years from 2001 to 2005, HETE-2 localized 50 bursts from SGR 1806-20 and 5 bursts from SGR 1900+14. The cumulative number-intensity distribution of SGR 1806-20 in the active year 2004 is well described by a power-law model with an index of -1.1 ± 0.6. It is consistent with previous studies, but burst data taken in other years clearly give a steeper distribution. This may suggest that more energetic bursts could occur more frequently in periods of greater activity. From the data, the spectral evolution during bursts with a time scale of ≳ 20 ms does not seem to be common in the HETE-2 sample. The spectra of all short bursts are well reproduced by a two blackbody function with temperatures of ∼ 4 and ∼ 11 keV. From a timing analysis to the SGR 1806-20 data, a time lag of 2.2±0.4 ms is found between the 30-100keV and 2-10keV radiation bands. This may imply (1) a very rapid spectral softening and energy reinjection, (2) diffused (elongated) emission plasma along the magnetic field lines in pseudo-equilibrium with multi-temperatures, or (3) a separate (located at ≲ 700 km) emission region of a softer component (say, ∼ 4keV), which could be reprocessed X-rays by higher energy (≳ 11 keV) photons from an emission region near the stellar surface.

本文言語English
ページ(範囲)653-678
ページ数26
ジャーナルPublications of the Astronomical Society of Japan
59
3
出版ステータスPublished - 2007
外部発表はい

ASJC Scopus subject areas

  • 天文学と天体物理学
  • 宇宙惑星科学

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